The present invention relates to a semiconductor device including a semiconductor acceleration sensor which converts displacement into an electrical signal by utilizing the piezoresistance effect exhibited by a semiconductor crystal such as a silicon crystal.
In recent years, with the development of micromachining technology, a semiconductor acceleration sensor is manufactured by forming a thin film on a semiconductor wafer and then etching it (Refer to IEEE Transactions on Electron Devices, Vol. ED-26, No. 12, December 1979, for instance).
FIGS. 3 shows a conventional semiconductor acceleration sensor manufactured by micromachining. FIG. 3A is a top view and FIG. 3B is a sectional view. A cantilever 51 and a weight 22 are formed by etching a semiconductor wafer 1. The cantilever 51 is made thinner than the other portions by etching. The cantilever 51 is deformed when receiving acceleration in the direction indicatedbyan arrow in FIG. 3B. The deformation amount of the cantilever 51 is detected through the piezoresistance effect exhibited by a diffusion resistor 21a that is formed on the top surface of the cantilever 51, and acceleration is determined through comparison with a diffusion resistor 21b. The diffusion resistors 21a and 21b are connected to high-concentration diffusion regions 55 and output terminals 23. A top stopper 53 and a bottom stopper 54 are provided to prevent breakage of the cantilever 51, and the entire structure is mounted on a ceramic substrate 52.
FIG. 4 shows a semiconductor acceleration sensor manufactured by micromachining which is disclosed in Japanese Unexamined Patent Publication No. Hei. 1-302167. A groove 62 is formed by etching in a cantilever 51 in the vicinity of a support 61 to provide a thin portion. Diffusion resistors 21 formed on the top face of the sensor constitute abridge circuit. Diffusion resistors 21c and 21d, which serve as reference resistors, are provided on the top face of the support 61. Diffusion resistors 21e and 21f, which serve as variable resistors for detecting the deformation amount of the thin portion, are so provided as to be perpendicular to the reference resistors.
The conventional semiconductor acceleration sensors are manufactured by etching. In particular, in order to increase the detection sensitivity, it is necessary to form the thin portion (the back face is processed). Since the thin portion is formed by etching, it is necessary to strictly manage the composition and the temperature of an etching liquid and stirring conditions in order to obtain uniform thickness, and additional manufacturing steps such as masking pattern formation are needed.
Further, since the diffusion resistors 21a and 21b are arranged and the weight 22 is formed on the top face of the acceleration sensor as shown in FIG. 3A, the top face of the acceleration sensor has a large area, which, for instance, restricts the number of sensors taken from one silicon wafer, causing a difficulty in reducing the manufacturing cost.
Also in the acceleration sensor of FIG. 4, to keep a sufficient level of strength of the thin portion, the width of a cantilever 51 and the width in the direction from this side to the deep side in the figure need a given value. Therefore, like the acceleration sensor of FIG. 3A, the area of the sensor top face of the acceleration sensor cannot be made small, which restricts the number of sensors taken from the semiconductor wafer 1, causing a difficulty in reducing the cost.
Further, since the diffusion resistors 21 for acceleration detection are provided on the face of the acceleration sensor which face is to receive acceleration, they need to be so arranged as to cause a large difference in resistance between the reference resistors that are located above the support 61 and the variable resistors.
The present invention has been made to solve the above problems, and an object of the invention is therefore to provide an inexpensive semiconductor acceleration sensor which can be manufactured easily and allows a large number of sensors to be manufactured from one semiconductor wafer 1, as well as to provide a manufacturing method for obtaining a pressure sensor.